Effects of Thrombin on the Potassium and ATP Content of Platelets *

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Abstract
Washed human platelets incubated in potassium-free buffer lost approximately 80% of their potassium, but this loss did not occur from platelets incubated in buffer containing potassium. Thrombin induced a rapid net loss of approximately 35% of the potassium from platelets incubated in buffer containing potassium. Calcium augmented the effect of thrombin on potassium loss from platelets to approximately 60%. These agents did not cause a net loss of potassium from human red blood cells. Trypsin was similar to thrombin in its effect on the loss of potassium from platelets, but plasmin had no effect. Studies employing radioactive potassium (K42) revealed equilibration of one-half to two-thirds of the potassium in the platelets with that in the surrounding media in control studies but with all of the potassium remaining after treatment with thrombin. The results suggest that potassium may be distributed within two compartments in the human platelet. Washed platelets exposed to thrombin or thrombin and calcium were depleted of 60 to 90% of their ATP. Platelets depleted of ATP by exposure to thrombin were capable of supporting clot retraction.